Technical Field
The present disclosure relates to a multilayer electronics assembly and an associated method of manufacture.
Description of the Related Art
Conventionally, multilayer printed circuit boards using epoxy fiberglass (FR4), fluoropolymer composites (such as polytetrafluoroethylene, PTFE), or mixed dielectric (MDk, a combination of FR4 and PTFE) have been used to route signals to components that are mounted on the surface of a multilayer structure. These multilayer printed circuit boards most commonly include traces that are etched copper as one means of routing signals to components. For these circuits, resistors can be screen-printed or etched. These multilayer printed circuit board assemblies can be used in a variety of applications including, among others, RF and power electronics modules. As one example, these technologies can form multifunction modules (MFM) which carry monolithic microwave integrated circuits (MMICs) on their surface.
In another conventional method, multilayer integrated circuits and microwave, multifunction modules, are constructed of multiple layers of fluoropolymer composite substrates that are bonded together into a multilayer structure by utilizing a fusion bonding process. The composite substrate material can be PTFE filled with glass fibers and ceramic. These multilayer structures may include thin film resistors that are screen printed or etched into the individual layers prior to the fusion process. For example, resistors can be etched into thin nickel phosphate films adjacent to copper layers, using a method that is similar to copper etching.
Certain discrete electrical circuit components, for example discrete devices, such as passive discrete resistors, capacitors, magnetic devices, and active semiconductor devices, are not merely thin films created by etching or screen printing. Instead, these discrete devices are attached to a substrate with, for example, a solder paste that cannot withstand the heat and/or pressure of the fusion bonding process. To incorporate such discrete electrical circuit components into a multilayer integrated assembly, the conventional method includes forming cavities in individual substrate layers, attaching the discrete electrical circuit components in the cavities, and applying a polymer bonding film layer as a separate, post-fusion bonding step. For example, U.S. Pat. No. 6,009,677 to Logothetis et al. and U.S. Pat. No. 6,395,374 to McAndrews et al. describe a process for manufacturing a multilayer structure of fusion bonded fluoropolymer composite substrates in which discrete electrical circuit components are attached post-bonding within cavities formed in the multilayer structure, and then covered with a film bonded layer.